The pathology of a number of human and animal diseases including hypertension, erectile dysfunction, coronary cerebral circulatory impairments, neurodegenerative disorders and cancer can be linked directly to changes in the actin cytoskeleton. These diseases pose a serious unmet medical need. The actin cytoskeleton is composed of a meshwork of actin filaments and actin-binding proteins found in all eukaryotic cells. In smooth muscle cells the assembly and disassembly of the actin cytoskeleton is the primary motor force responsible for smooth muscle contraction and relaxation. In non-muscle cells, dynamic rearrangements of the actin cytoskeleton are responsible for regulating cell morphology, cell motility, actin stress fiber formation, cell adhesion and specialized cellular functions such as neurite retraction, phagocytosis or cytokinesis (Van Aelst, et al. Genes Dev 1997, 11, 2295).
The actin cytoskeleton is controlled by a family of proteins that are a subset of the Ras superfamily of GTPases. This subset currently consists of RhoA through E and RhoG (refereed to collectively as Rho), Rac 1 and 2, Cdc42Hs and G25K and TC10 isoforms (Mackay, et al. J Biol Chem 1998, 273, 20685). These proteins are GTP (guanine nucleotide triphosphate) binding proteins with intrinsic GTPase activity. They act as molecular switches and cycles between inactive GDP (guanine nucleotide diphosphate) bound and active GTP bound states. Using biochemical and genetic manipulations, it has been possible to assign functions to each family member. Upon activation the Rho proteins controls the formation of actin stress fibers, thick bundles of actin filaments, and the clustering of integrins at focal adhesion complexes. When activated the Rac proteins control the formation of lamellopodia or membrane ruffles on the cell surface and Cdc42 controls filopodia formation. Together this family of proteins plays a critical part in the control of key cellular functions including cell movement, axonal guidance, cytokinesis, and changes in cell morphology, shape and polarity.
Depending on the cell type and the activating receptor, the Rho proteins can control different biological responses. In smooth muscle cells, Rho proteins are responsible for the calcium sensitization during smooth muscle contraction. In non-smooth muscle cells the Rho GTPases are responsible for the cellular responses to agonist such as lysophosphatidic acid (LPA), thrombin and thromboxane A2 (Fukata, et al. Trends Pharcol Sci 2001, 22, 32). Agonist response is coupled through heterotrimeric G proteins Galpha12 or Galpha13 (Goetzl, et al. Cancer Res 1999, 59, 4732; Buhl, et al. J Biol Chem 1995, 270, 24631) though other receptors may be involved. Upon activation Rho GTPases activate a number of downstream effectors including PIP5-kinase, Rhothekin, Rhophilin, PKN and Rho kinase isoforms ROCK-1/ROKbeta and ROCK-1/ROKalpha (Mackay and Hall J Biol Chem 1998, 273, 20685; Aspenstrom Curr Opin Cell Biol 1999, 11, 95; Amano, et al. Exp Cell Res 2000, 261, 44).
Rho kinase was identified as a RhoA interacting protein isolated from bovine brain (Matsui, et al. Embo J 1996, 15, 2208). It is a member of the myotonic dystrophy family of protein kinase and contains a serine/threonine kinase domain at the amino terminus, a coiled-coil domain in the central region and a Rho interaction domain at the carboxy terminus (Amano, et al. Exp Cell Res 2000, 261, 44). Its kinase activity is enhanced upon binding to GTP-bound RhoA and when introduced into cells, it can reproduce many of the activities of activated RhoA. In smooth muscle cells Rho kinase mediates calcium sensitization and smooth muscle contraction and inhibition of Rho kinase blocks 5-HT and phenylephrine agonist induced muscle contraction. When introduced into non-smooth muscle cells, Rho kinase induces stress fiber formation and is required for the cellular transformation mediated by RhoA (Sahai, et al. Curr Biol 1999, 9, 136). Rho kinase regulates a number of downstream proteins through phosphorylation, including myosin light chain (Somlyo, et al. J Physiol (Lond) 2000, 522 Pt 2, 177), the myosin light chain phosphatase binding subunit (Fukata, et al. J Cell Biol 1998, 141, 409) and LIM-kinase 2 (Sumi, et al. J Bio Chem 2001, 276, 670).
Inhibition of Rho kinase activity in animal models has demonstrated a number of benefits of Rho kinase inhibitors for the treatment of human diseases. Several patents have appeared claiming (+)-trans-4-(1-aminoethyl)- 1-(pyridin-4-ylaminocarbonyl)cyclohexane dihydrochloride monohydrate (WO-00078351, WO-00057913) and substituted isoquinolinesulfonyl (EP-00187371) compounds as Rho kinase inhibitors with activity in animal models. These include models of cardiovascular diseases such as hypertension (Uehata, et al. Nature 1997, 389, 990), atherosclerosis (Retzer, et al. FEBS Lett 2000, 466, 70), restenosis (Eto, et al. Am J Physiol Heart Circ Physiol 2000, 278, H1744; Negoro, et al. Biochem Biophys Res Commun 1999, 262, 211), cerebral ischemia (Uehata, et al. Nature 1997, 389, 990; Seasholtz, et al. Circ Res 1999, 84, 1186; Hitomi, et al. Life Sci 2000, 67, 1929; Yamamoto, et al. J Cardiovasc Pharmacol 2000, 35, 203), cerebral vasospasm (Sato, et al. Circ Res 2000, 87, 195; Kim, et al. Neurosurgery 2000, 46, 440), penile erectile dysfunction (Chitaley, et al. Nat Med 2001, 7, 119), central nervous system disorders such as neuronal degeneration and spinal cord injury (Hara, et al. J Neurosurg 2000, 93, 94; Toshima, et al. Stroke 2000, 31, 2245) and in neoplasias where inhibition of Rho kinase has been shown to inhibit tumor cell growth and metastasis (Itoh, et al. Nat Med 1999, 5, 221; Somlyo, et al. Biochem Biophys Res Commun 2000, 269, 652), angiogenesis (Uchida, et al. Biochem Biophys Res Commun 2000, 269, 633; Gingras, et al. Biochem J 2000, 348 Pt 2, 273), arterial thrombotic disorders such as platelet aggregation (Klages, et al. J Cell Biol 1999, 144, 745; Retzer, et al. Cell Signal 2000, 12, 645) and leukocyte aggregation (Kawaguchi, et al. Eur J Pharmacol 2000, 403, 203; Sanchez-Madrid, et al. Embo J 1999, 18, 501), asthma (Setoguchi, et al. Br J Pharmacol 2001, 132, 111; Nakahara, et al. Eur J Pharmacol 2000, 389, 103), regulation of intraoccular pressure (Honjo, et al. Invest Ophthalmol Vis Sci 2001, 42, 137) and bone resorption (Chellaiah, et al. J Biol Chem 2000, 275, 11993; Zhang, et al. J Cell Sci 1995, 108, 2285).
The inhibition of Rho kinase activity in patients has benefits for controlling cerebral vasospasms and ischemia following subarachnoid hemorrhage (Pharma Japan 1995, 1470, 16).